Doyle — Some Researches in Experimental Morphology . 411 



In this way it was hoped to determine, if possible, how far the changes 

 resulting in the petiole were due to the influence of the grafted sprout, how 

 far due to changes in the relation of the petiole with the mother-plant, how 

 far due to increased duration of life of the petiole. 



III. — The Changes in the Petiole. 

 A . — 3facroscopic. 



As the grafted sprout grew and enlarged, distinct changes were apparent 

 in the petiole. Week by week it increased in diameter, and finally assumed 

 for all intents and purposes the diameter of the stem above or below. In 

 Pelargonium, be it noted, the diameter increase, save in one instance, 

 was much greater in the vertical than in the horizontal direction. By 

 the time the small grafted bud had become a shoot about two feet high, 

 tlie petiole had assumed the proportions as well as the functions of a stem. 

 The increase in diameter was obviously due to an internal tissue increase, as 

 in every case the outer tissue was burst in slits, the slits becoming protected 

 by well-developed cork masses. A series of pictures will demonstrate this 

 increase in size more clearly than any description. 



Plate XXVIII, fig. 3, is Pelargonium zonule v. meteor, A, 1390,3/5. It 

 was photographed on January 7th, 1914. It is fairly weak, but was selected 

 for photography as showing the petiole-become-stera very clearly. Wliat 

 appears to be the branch leaving the top at right angles is the petiole, a sliort 

 distance along which the swelling at the grafting-place can be seen. All 

 above tliis is the growth of tlie small grafted bud. 



Plate XXVIII, fig. 4, is a near view of the petiole seen in Plate XXX, 

 fig. 2. The whitish mass on tlie upper side of the petiole is tlie cork mass 

 which developed where the upper corticle tissues became split. The V-line 

 of the wedge-graft can be clearly seen. The grafting zone is singularly free 

 from graft callus. 



Plate XXIX, fig. 1, is Solanum Richardi, A, 1301, 10/4. It was photo- 

 graphed on June 21st, i.e., little more than two months from the date of 

 grafting. The main stem is at the bottom in the middle ; the small lateral 

 branch on the right is the petiole. As we see, its dimensions all but equal 

 that of the mother stem. If we follow up the swollen petiole, we come to a 

 swelling. This is a mass of graft callus, and indicates the position of the 

 grafting zone. All above this zone was developed from the grafted buds. 

 This shows with what rapidity results may be obtained by this grafting 

 method. 



